Implemented a caching API to query chunkserver status

[fsareshwala]

GitHub user [echenj|https://github.com/echenj] has created an issue on our public [GitHub Issues|https://github.com/quantcast/qfs/issues] list.

This ticket is a mirror of the first post of the public ticket on github. The purpose of this ticket is to have an owner of the public response. The owner is responsible for researching the answer and responding to the public issue in a timely manner.

#46

Issue Description
{code}
The metaserver ping function has been modified to include a caching system. The ping function itself has also been modified to return a Status object instead of modifying the Status passed as a parameter. The cache refresh time is 30 seconds, but will not refresh unless a user asks for data. The added queries will pull information from the cache.
The three new queries are:

• /query/stats/<hostname/ip>
  • Displays all of the attributes for any UpServer instance
• /query/dead/<hostname/ip>
  • Displays the current status of any server, and also the entire disconnect history
• /query/dead/count
  • Displays all of the servers that have any recorded disconnects and their disconnect counts
    {code}